Venetian blind slat and method of and apparatus for forming the same



1943- A. B. WILSON 2,313,111 VENETI'AN BLIND SLAT AND METHOD OF AND APPARATUS FOR FORMING THE SAME Filed July 26, 1940 s Sheet s-Shet 1 F I I yQN A. B. WILSON March 9, 1943.

VENETIAN 131.1111) SLA'I AND METHOD OF AND APPARATUS FOR FORMING THE SAME Filed July 26, 1940 s Sheets-Sheet 2 u mm Marh 9, 1943. 2,313,111 VENETIAN BLIND SLAT AND METHOD OF AND APPARATUS FOR FORMING THE- SAME B. WILSON Filed July 26, 1940 3 Sheets-Sheet 3 Patented Mar. 9, 1943 VENETIAN BL'IND SLAT AND METHOD OF AND APPARATUS FOR FORMING THE SAltIE Allen B. Wilson, Evanston, lll., assignor to Acme Steel Company, Chicago, 111., a corporation .0!

Illinois Application July 26, 1940, Serial No. 347,592

8 Claims.

This invention relates to improvements in methods of and apparatus for forming Venetian blind slats from strip steel or the like, whereby durable slats of novel form and attractive appearance may be quickly and economically produced.

The use of Venetian blinds has increased greatly in recent years and there has been a growing tendency to employ metal slats in the construction of these blinds in order to avoid the heavy and cumbersome appearance which wooden slats usually have when they are of sufficient thickness to possess the required strength. Metal slats, when formed of strip steel, for example, may be made very thin but, in order that they may have suflicient stiffness to prevent sagging between their ends, it is necessary that they have a curved or other non-planar cross section and inapplicants copending application, Serial No. 239,229, filed November 7, 1938, there is disclosed an improved method of and apparatus for forming Venetian blind slats of curved cross section in a speedy and economical manner without resorting to a several-stage rolling process and without excessive stretching of the metal, whereby metal slats of thin and hard material are produced which are stifi and straight with parallel longitudinal edges. i

The present invention includes the discovery that metal Venetian blind slats having other transverse cross sections adapted to give the necessary stiil'ness to the slats such, for example, as a cross section having the form'of a double reverse curve, similar to a flattened letter S, and other cross sections comprising a plurality of curvatures, may be quickly and economically formed by a rolling and bending process which is carried out in two stages. The first stage of the improved process is like the first stage of the process disclosed in said prior application and involves the stretching of the metal strip in the region between its edges, leaving the edge portions unstretched, so that the intermediateportion of the strip has an elongated buckled appearance. This first stage performs the function of standardizing and rendering more or less uniform in kind or character the;irregularities initially present in the metal strip, fso that it can be worked during the second stage to produce predetermined results. If the strip metal were perfectly formed with a uniform thickness and with all of its surfaces flat and no irregularities present, it would be possible to impart an S- sliaped or other multi-curved cross section to a hard metal strip without any preliminary stretching, but this perfection is lacking in commercial strip steel and the like even when it is carefully made with the best modern equipment, and it has present therein a great number of irregularities of varying magnitude and character such as relatively long edges, pockets or depressions at intermediate points, and the like. It has been discovered that if the central portion of the metal strip be stretched longitudinally to effect a permanent elongation, the irregularities may thereby be transformed into a uniform kind or character of irregularity, namely a permanent central or intermediate elongation, which will permit subsequent bending and stretching operations to be performed with uniform and predetermined results. The necessary elongation of the intermediate portion of the strip will be effected when it is subjected to sufficient tension to cause a condition of the stresses in the metal such that if the tension were relieved, all of the said intermediate portions of the strip would be under compression. That condition of the stresses may, of course, result in part from a previous relative elongation of individual portions of the strip in the process of its original manufacture, but is brought about mainly by the elongation effected by the tension to which the strip is subjected in the first stage of the process. When that condition has been created inthe strip, the second stage of the process will cause the stripto assume with certainty an sshaped or other selected non-planar cross section and a predetermined longitudinal shape,

such as a straight form having parallel longitudinal edges.

In the second stage of the process, the metal is moved endwise and bent transversely while at the same time stretching longitudinally diilerent longitudinal portions of the strip in varying degree, depending upon the form of the cross section to be produced. If an S-shaped cross section is to be formed, for example, this being a desirable form because of the attractive appearance of the slats in the finished blind structure, the elongated metal strip, which has had its center portion stretched longitudinally in the first stage of the process, is bent transversely in opposite directions on oppositesides of its longitudinal center line to cause it to assume an s-shaped form, and is stretched longitudinally on opposite sides of said center line to an increasing degree from the center line outwardly, while the strip is confined to the S-shaped form, the strip while being thus bent and confined being supported in advance of and immediately following the region of confinement and transverse bending in order to control the stretching of the metal and to insure that the resulting product will be straight with parallel edges. It has been found that in order to enable the strip having an 8- shaped cross section to assume and retain a straight form upon passing through the second stage of the process, it is necessary that the stretching of the central portion of the'strip,

The material used in the practice of themethod of the present invention is preferably fiat strip steel which is comparatively hard and thin. "I'his steel should be somewhat resilient so that the finished slats will return to their proper shapes when bent therefrom, but it should be sufilciently ductile to enable it to retain a permanent set when it assumes its final form at the end of the second stage of the process.' The two stages of the process need not necessarily be carried outin quick succession or at the same place. For example, the first stage of the process may be practiced by a strip steel manufacturer who may sell the product of that stage of the process to a manufacturer of Venetian blinds who will then perform upon that product the operations constituting the second stage of the process.

One olgeot of the invention is to provide a metallic enetian blind slat having a transverse cross section made up of a plurality of concave and convex curves.- Another object is to provide a metallic Venetian blind slat oi S-shaped cross section. A further object is to provide an improved method of forming Venetian blind slats of substantially S-shaped cross section according to which afiat metal strip is subjected to a rolling and bending process which involves the successive stretching of different longitudinal portions of the strip. Still another object is to provide an improved method of forming Venetian blind slats by a two-stage process having the characteristics pointed out above. Another object is to provide improved apparatus for forming Venetian blind slats of novel form from fiat metal strips of steel or other suitable material. Other objects relate to various features of construction of the improved apparatus and to various details of the method which will appear more fully hereinafter. 1

The nature of the invention will be understood from the following specification taken with the accompanying drawings, in which one form of the improved apparatus embodying the present invention is disclosed in connection with the illustration of one example of the novel method of forming the improved Venetian blind slat of the present invention. In the drawings,

I Figure 1 shows a somewhat diagrammatic side elevation of one form of the apparatus, constituting a part of the present invention, which may be, employed'in straightening an elongated metal strip and stretching the central portion thereof longitudinally preliminary to imparting thereto an S-shaped' cross section which is formed by a later stage of'the process;

on the line 3-3 of Fig. 2

pa'ratus shown inbuckled eflect which has been produced by faceflat and its edges Fig. 2. shows an enlarged vertical section 76 through a portion or the apparatus illustrated in Fig. 1, illustrating the straightening and stretching rolls and portions of adjacent friction rolls around which the strip to the reel on which the stretched strip is wound;

Fig. 3 shows an enlarged vertical section taken Fig. 4 shows an enlarged verticalseet ion taken on the line 4-4 of Fig. 2;

. Fig. 5 shows an enlarged-side elevation of the metal strip after it has passed through the ap- Figs. 1 and 2, illustrating the stretching longitudinally the central portion of the strip; 7

v Fig. 6 shows a top plan view of a portion of the strip illustrated in Fig. 5

Fig. 7 shows an enlarged :prlncipal parts of the apparatus which is employed in carrying out the second stage of the process during which the elongated'metal strip having the form shown in Fig 5 and 6 is bent, confined and stretched in order to impart thereto a substantially S-shaped cross section;

Fig. 8 shows a horizontal section taken on the line 8-8 of Fig. 7;

Fig. 9 shows an enlarged detail section-0n the line 9-9 of Fig. 7 showing the supporting guides which engage the elongated strip as it passes through the [rolls by which the S-shaped co'nfiguration is imparted to it; Fig. 10 shows a side elevation of one of the shoes shown in Fig. 9;

Fig. 11 is a vertical section taken on the line ll-Il of Fig. 7 showing the configuration of the rolls in the plane where they engage the strip; Fig. 12 is a sectional view taken on the line 12-12 of Fig. 7 showing, among other things, the rolls which support and guide the strip as it emerges from the rolls which impart the shaped cross section thereto;

Fig. 13 shows a top plan view of the metal strip in its final form after the S-shaped cross section has been imparted thereto by the second stages of the process; and

Fig. 14 shows a sectional view taken on the line llll of Fig. 13.

side elevation of the Although the strip material employed in the.

practice of the present invention may initially be in a substantially perfect condition with its surparallel to each other, it frequently happens that curvature in its own plane, known as camber, and the apparatus of the present invention is therefore preferably constructed to eliminate this camber in the strip' preliminary to stretching the intermediate portions of the strip longitudinally in the first stage of the process. The method and apparatus for removing the camber in the metal strip do not in themselves constitute a part of the present. invention as they are claimed in the United States Patent No. 2,140,533, granted December 20, 1938, on an application of Chester M. MacChesney. In the apparatus shown in Figs. 1 to '4, inclusiv of the drawings, the. elongated metal .strip l5, of steel or the like, is shown as being withdrawnfrom a reel I 6 and moved in the direction of the arrow I! by means of a series of driven friction rolls 18 which are comparatively large in diameter and which are arranged in zigzag fashionv so' that the strip is compelled to follow an irregular path when passing through this series of rolls, thereby obtaining a large area of contact between the strip and the surface of passes from a supply reel strip metal has a lateral' each roll. The strip l then passes in zig-zag fashion through a series of parallel straightening rolls l9 which are comparatively small in diameter and which operate as idler rolls, being arranged with their axes in one plane so that the strip is bent back and forth between these rolls as it passes through them on opposite sides of successive rolls. Although the strip is preferably restrained against lateral movement as it passes through these rolls, as explained in said application of Chester M. MacChesney, it has been found desirable when operating upon strip metal of very fine gages, which are preferably used in the manufacture of Venetian blind slats, to permit some lateral movement of the strip while it is being straightened. After passing through the straightening rolls IS, the strip then passes through a series of friction rolls which are power driven and which pull the strip l5 under tension through the rolls l9. Upon emerging from the rolls 20, the strip I5 is wound upon a reel 2|, which is power driven and which maintains the strip under sufiicient tension in the process of winding to hold it'ln contact with the friction rolls 20. The friction rolls 20 are preferably slightly larger in diameter than the'rolls i8, if the rolls of these two series are driven at the same angular speed, or the rolls 20 are driven slightly faster than the rolls i8, so that the peripheral speeds of the rolls 20 are greater-than the peripheral speeds of the rolls i8, thereby creating a substantial tension in a longitudinal direction in the strip l5 as it passes through the intervening straightening rolls l9. Some slippage is provided in the driving mechanism of the friction rolls so that the tension created in the strip l5 is-not sumcient to elongate-the strip generally throughout its width and the result is that, as the strip passes through the rolls I9, the tension therein is sufficient to stretch the shorter edges .of the strip until these shorter edges are of the same length as the opposite longer edge portions, as set forth in said patent of ChesterM. MacChesney. A brake is applied to the supply reel It to prevent the metal strip from being drawn therefrom too rapidly, thereby maintaining it inclose contact with the rolls l8, and the driving mechanism which is connected to the winding reel 2! is provided with a friction clutch which is adapted to slip when required, so that, if the reel 2! be driven at a greater speed than the friction rolls 20, as is the preferable practice, the friction clutch may slip and at the same time maintain the metal strip sufficiently taut between the rolls 28 and the reel M to bring about a tight winding of the strip in the coil and at the same time to keep the strip in close contact with the surfaces of the rolls 20.

The friction rolls it are mounted on shafts 23 which are preferably geared'together so that they rotate in unison at the same speed and the friction rolls 20 are mounted on shafts 24 which'are also preferably geared together so that they are driven in the proper directions at the same speed. Each series of shafts 23 and 24 is power driven and the driving mechanism of the two series of shafts may be connected together by a belt orthe like so that they will operate in unison, although the arrangement is preferably such that the rolls 20 are driven at a slightly greater speed than the rolls [8 and some slippage in the belt or other connecting mechanism is provided to take care of the difference in the driving tension will at'all times be maintained in the strip passing'through the rolls.

- speeds so that angle bar secured upon a base 26 by means of their proper spaced relations.

studs 21, as shown in Figs. 3 and 4. This frame 25 has an upwardly extending flange 25a in which are secured the inner reduced ends 30a of a series of stationary spindles or axles 30 upon which the rolls l9 revolve. These spindles are provided adjacent thei inner ends with integral surrounding collzrs 301) which coact with the outer face of the frame member 25 and the inner threaded extremities of the spindles are engagedby nut 3| for clamping the spindles securely in position on the frame. Each roll i9, except the last roll of the series, at the left as viewed in Fig. 2, is in the form of a cylindrical sleeve adapted to revolve about the body portion of one of the spindles 30. Bushings 32 are mounted in each of the rolls l9 to coact with the supporting spindle 30 and the outer reduced end of each spindle is threaded to receive a washer 33 and a nut 34 by which the roll is held in place on the spindle. The outer extremity 300 of each spindle, upwardly of the threaded portion, has a smooth thin cylindrical surface to engage one of a series of apertures in a supporting framemember 35 which is provided with transversely extending threaded holes to receive a number of set .screws 36 by which this frame member is clamped in position on the outer end of the spindles to hold them against vibration and in The spindles 30 are located with their axes in a single horizontal plane and the metal strip I5 is carried under one roll and over-the next one throughout the series of rolls so that the strip is compelled to follow a sinuous path which results in stretching the shorter edge portions of the strip whereby t e edges assume the desired parallel relations ip and the surface becomes substantially fiat andfree of irregularities. The rolls l9, which are of the cylindrical form described above, are of the same size and in alignment with each other but they may bereplaced by other rolls of difierent 1 sizes when it is desired to operate upon metal strips of different widths. The roll is which is located nearest to the friction rolls i8 is provided with end collars or flanges tab which are comparatively large in diameter so that the strip is preferably guided in its passage to the rolls as from the rolls E8.

The roll i9 which is nearest to the friction rolls 26, being the last roll of the series of rolls is, is constructed and mounted in the same manner as the other rolls i9 except that its outer peripheral surface is transversely curved, as shown at H90 in Fig. 3, thus giving this roll a con vex outer surface which is symmetrical on opposite sides of a plane passing through its middle point transversely to its axis, so that as the metal strip passes over this roll the portion of the strip between its lateral edges is stretched longitudinally of the strip to give it a greater length than the edge portions of the strip. The strip thus'assumes the form shown at ii'w. in Figs. 5 and 6 wherein the portions of the strip between its lateral edges are adapted to buckle out of a plane containing the edges of the strip due to their greater length. This strip material having its central portion elongated is the product of the first stage of the process and may be supplied in coils to Venetian blind manufacturers who subject it to the second stage of the process, now I to be described, which imparts to the strip an S-shaped cross section.

follow immediately after the first stage, the metal strip l5 having its intermediate portion elongated is subjected to a transverse bending action by a continuous rolling operation which stretches the lateral portions of the strip on opposite sides of its longitudinal center line to such an extent that all parts of these lateral portions, at the conclusion of the second stage of the process, are stretched longitudinally to the same extent that the central portion of the strip was stretched during the first stage of the process. of course, the stretching ellected by the first stage of the process extends laterally from each side of the center line and the lateral edges are the only portions which remain unstretched so that, during the stretching operation eifected by the second stage of the process, the longitudinal stretching of the metal increases gradually from the longitudinal center line outward- ]y and the lateral edges of the strip are the only parts which are stretched in the second stage of the process to thesame extent that the longitudinal center line of the strip was having the forms shown in Figs. 5 and 6, it is passed through a pair of forming rolls 46 and 4 I,

shown in Figs. 7 to 10, inclusive, which are mounted one above the other and arranged to be driven in the direction of the arrows 42 shown in Fig. 7. The roll 40 is provided at one side with an annular projection 40a having a rounded con .vex surface and it is provided at the other side with a corresponding annular depression 40b.

Similarly, the roll 4| is provided with an annular projection lid and an annular depression or recess 4|b. The projections 4M and HG. are of the same size and of the same surface configuration and the annular depressions 40b and llb are also of the same'size and surface configuration as the projections 60a. and Ma so that the rolls 40 and 4| are adapted to intermesh with 2,318,111 In the second stage of the process, which may in conjunction with the bending action of these rolls to effect a longitudinal stretching of the metal on opposite sides of its longitudinal center line. In order to effect the working of thin metal in this manner, it is necessary that the curved sections formed inthe metal by the forming rolls be of considerable depth so that the strip will have substantial stiffness between the forming rolls and said supports and also because the curvatures tend to flatten out after the strip passes the forming rolls so that the initial curvatures must be greater than those desired in the final'product. It is also desirable that'these supports be located as close as possible to the periphieral surfaces of the forming rolls. In order that the stretching of the metal which is thus efiected may be regulated, the supports for the strip are made adjustable so that the pressures exerted by them on the strip may be varied.

At the entrance side of the rolls, the supporting means takes the form of a pair of shoes 45 and 48, shown in Figs. 7, 9 and 10, which are provided with convex surfaces 45a and 46a, respectively, to coact with correspondingly curved surfaces on the upper and lower sides of the strip |5a in advance of the rolls 40 and 4|, as shown in Fig. 9. At this point, due to the action of the formingrolls, the strip |5a assumes a transverse cross section which is curved in the same manner as the curvature of the strip between the rolls 40 v and ti but in a lesser degree, and the rounded and retain a surfaces 45a and 46a are shaped to conform to the curvatures which the lateral portions of the strip assume at this point. The shoes 45 and 46 are curved on the sides away from the strip to correspond with the curvatures of the rolls and they terminate in rounded extremities at their free ends which enter the recess between the rolls, as shown in Fig. 8. They are pivotally mounted upon the studs 41 and 48, respectively, which threadedly engage the free ends of two supporting bars 48 and 50, respectively. These bars 49 and 5|! are pivoted at their other ends, as shown at 5|, upon an upright supporting frame member 52 in which the shafts 43 and 44 are mounted. In order to adjust the elevations of the shoes 45 and 46, the bars 49 and 50 are provided adjacent their free ends with blocks 53 and 54, respectively, which are adapted to be engaged by certain adjusting mechanism. This adjusta 'ing mechanism comprises a sleeve 55 which each other, as shown in Fig. 10. with the pro- J'ection 40a entering the recess 4!!) and the projcction 4|a. entering the recess 40b. The rolls and 4| are spaced apart sufliciently to receive between them the metal strip |5a and they are mounted upon the shafts 43 and 44, respectively, which are power driven so that the rolls 45 and 4i, which are of the same diameter, rotate in unison at the same peripheral speeds and move the strip longitudinally between them. The transverse curvatures of the registering parts 40a--4|b and 4Ia-40b are preferably greater providing a three point support for each longitudinal half-portion of the strip which operates threadedly engages the block 53 engages the block 54. The sleeve 55 is provided at its upper end with a hand wheel 55a. and the properly cooperating with the forming rolls and with the supports following those rolls to eflect the desired stretching of the lateral portions of immediately following the forming rolls, thereby the strip.

The mounting of the shoes 45 and 46 on the studs 4] and 48 permits these shoes to be replaced by others when strips of diflerent widths are to be treated by the apparatus, and the rolls 40 and 4| are alsopreferabiy mounted for such replacemenwbeing spaced by sleeves 59 from the frame member 52 in which the shafts 43 and 44 Y and a rod 56, mounted within the sleeve 55, which threadedly are Journaled. The projecting ends of the shafts 43 and 44 are connected to a source of power, not shown, to be driven in unison. By employing shafts 43 and 44 of various lengths, the rolls 40 and 4| may be selected for the treatment of metal strips of various widths and thicknesses.

The means for supporting and controlling the strip |5a as it emerges from the rolls 40 and 4| comprises a pair of small rollers GI and 62, shown particularly in Figs. '7, 8 and '12, which are provided with convex outer surfaces 6 la and 62a for engagement with the corresponding surfaces of the strip. The two rollers 6| and 62 are offset from each other laterally and are positioned on opposite sides of the strip I50. so that each roller engages one of the longitudinal recesses in the S-shaped strip. The roller 6| is mounted betweencollars on a stud 63 and the roller 62 is mounted between collars on a stud 64, the inner ends of these studs being secured in the free ends of pivotally mounted supporting bars 65 and 66,

respectively. Each of these bars 65 and 66 is .mounted on a pivot pin 61 carried by the frame member 52 and the free ends of these bars have secured thereto a pair of blocks 69 and 10, re-

spectively, which are engaged by mechanism similar to that previously described for rocking the bars about their pivots and thereby regulating the elevation of the rollers BI and 62. This mechanism comprises a sleeve I I having a threaded engagement with the block 69 and having journaled therein a rod 12 which has a threaded engagement with the block 10. The sleeve H is journaled in a bearing block 13 carried by the frame member 52,- and the sleeve and the rod are provided at their upper ends, respectively, with hand wheels Ho. and 12a. which may be turned to regulate the positions of the rollers 6| and 62.

In the practice of the present invention, the strip is supported on the concaved surfaces thereof on opposite sides of its longitudinal center line, and with the proper adjustment of these supporting means 45 and 46 and 6| and 62, the support takes the form of a pressure or reaction tending to twist the strip about its longitudinal center line, since two of the supporting members 45 and 6| are on one side of the strip and the other supporting members 46 and 62 are on the other side of the strip. As a result of these supporting pressures, applied on opposite sides of the longitudinal center line of the strip and on opposite sides of the forming rolls 40 and 4|, tensile stresses are set up in the strip acting between the edge portions of the concaved parts of the strip between these forming rolls and those intermediate portions of the strip which are engaged bythe supporting means, and these stresses act in conjunction with the bending action of the rolls 40 and 4| to cause a longitudinal stretching of the portions of the strip on opposite sides of its longitudinal center line. During this. action, the center line of the strip moves substantially along a linear path of travel and the twisting action on the strip is limited due to the close spaced relation of thesupports to the forming rolls, and this puts a limit upon the permissible stretching of the central portion of the strip in the first stage because the longitudinal stretching of the lateral portions in the second stage, which is controlled by the twisting action, must be sufficient center stretching and maintain the strip straight with parallel edges. If the twisting action is too limited the strip to balance the previous will not be straight with parallel thing which may best be determined by trial in advance of the first stage. It varies with the thickness and width of the strip. For illustration, and by way of example, if the strip to be used in the practice of the process is a steel strip 2%,; inches wide and 0.008 inch thick, which are desirable dimensions for Venetian blind purposes, and it be assumed that a strip three feet long is passed through the first stage of the process, the intermediate portion of that strip should be elongated until it is from 0.005 to 0.015 inch longer than the lateral edges thereof, measured along the longitudinal center line of the strip. That degree of elongation is satisfactory and similar ranges of elongation can readily be determined for strips of different widths and different thicknesses. If the intermediate portion of the strip be elongated too much, there .is a tendency for the strip to twist about its longitudinal center .line when itis subsequently bent and stretched in the second stage of the process to produce an S-shaped cross section, but the proper limit of permanent elongation of the intermediate portion to produce the best results may readily be determined by trial.

Assuming that the process is being carried on with a steel strip 2%, inches wide and 0.008 inch thick, as mentioned above. the dimensions of the the accompanying drawings. Each roll should be two inches wide. The concaved portion of each forming roll should be. formed with a radius 11 of 0.635 inch and the convex portion of each roll should be formed with a radius 'l'l of 0.625 inch.

Theshoes 45 and 46 which guide the metal strip to the rolls 40 and 4| should preferably be 2 inches long, as shown by the numeral 18 on the accompanying drawings. Each block 45 and 46 should be one inch wide, as shown by the numeral 19 on the drawings, and the vertical thickness of the body portion of the block, shown by the reference numeral 80, should preferably be about 0.950 inch. The curved surface of the body portion of each block should preferably be formed by radii 8| and 82, shown, in the drawings, which are 1 inches and 64inch, respectively. The radius 83 of the outer surface of each block 45 and 46 which conforms generally to the curvature of one of the rolls 40 or 4| should preferably be about 2.609 inches, as shown in Fig. 10. These blocks are directed oppositely, as shown in Fig. 9, with the parts formed by the radii 5| in proximity to each other. These blocks '45 and 46-should pref erably be so mounted that the axes of their pivots 41 and 48 are located in a vertical plane which plane containing the -tion in the same vertical plane and with this plane located a distance of 2% inches from the above-mentioned plane containing the axes of the shafts 43 and 44. When operating upon a steel strip having the initial dimensions mentioned above, the rollers 6i and 62 should preferably have maximum outside diameters of 1.120 inches, as indicated by the numeral 84 shown in Fig. 8, and they should be inch wide, measured parallel to their axis of rotation, with the edges of their peripheral surfaces rounded 011, as shown in Fig. 12, and so that they will conform to the curvature of the metal strip at the place where they are located without tact between the strip tions.

In general, as stated above, it is desirable to locate the supporting shoes '45 and as close as possible to the peripheral surfaces of the rolls Bo and 4| and to cause them to project into the and their lateral edge porconverging space between the peripheries of these rolls as far as possible, thus limiting the distance through which the strip has to be maintamed-comparatively stifi', due to its concavity, in order to cause the metal to be stretched by the forming rollsand the preceding and following supports. Similarly, it has been found desirable to locate the supporting rolls 6i and 62 in close proximity to the peripheral surfaces of the rolls 40 and ll and the dimensions which have been given above are those which have been found to give satisfactory result when operating upon a steel strip having the dimensions stated. With this example, the desirable dimensions for operating upon strips of other widths and thicknesses may readily be determined.

Although oneform of the improved Venetian blind slat and one example of the improved method of forming it have been illustrated and described in connection with the disclosure of one example of the improved apparatus employed in forming the slat, it will be understood that the improved slat and the apparatus used in forming it may be varied in construction and that the method may be practiced in various ways with out departing from the scope of the appended claims. In some of the claims, the condition 01 having an actual conthe metal strip at the end of the first stage of the process is defined by reference to the stresses existing therein, which is merely one way of defining the permanent elongation of a portion of the strip which is eflected by that stage, and the portion which is elongated is defined as the portion between the edges or as an intermediate por tion but it will be understood that these definitions are to be construed in the light of the practical results accomplished and that a process or apparatus is to be considered as within the scope of such claims even though the elongation effected in the first stage is not precisely coextensive with the width of the strip and even though slight portions of the original irre ularities may still remain in the strip, as it has been found that satisfactory straight metal strips of the desired cross section may be produced when substantial portions at the edges of the metal are not elongated in the first stage of the process and when slight original irregularities still re- 1118111.

I claim:' 1. A Venetian blind slat comprising a strip of thin flexible resilient steel having its central portion stretched longitudinally with the portions sides of said center line being stretched longi tudinally in sufiicient amounts to maintain the slats straight with parallel edges.

2. The method of forming a metal strip of predetermined longitudinal shape and a cross section having a plurality of curvatures, which comprises the operations of stretching longitudinally the intermediate portion of a thin elongated metal'strip by subjecting said intermediate portion to longitudinal tension of such magnitude that if the tension were released all parts of the metal of said intermediate portion would be under compression, and then moving the strip longitudinally and bending it transversely into a cross section made up of a plurality of curvatures and simultaneously applying pressure to,

ing Venetian blind slats, of means for stretching longitudinally the intermediate portion of an elongated metal 'strip, means for moving said strip longitudinally and bending it to form an s-shaped cross section in the strip, means for supporting the strip on its opposite surfaces on opposite sides of its longitudinal center line in advance of and following the place of bending to cause the lateral edge portions of the strip to be stretched longitudinally, and means for adjusting said supporting means to vary the pressure thereof upon said strip.

4. The combination in apparatus for forming Venetian blind slats, of a pair of forming rolls each provided with an annular projection and an annular recess, the projection on one roll being arranged to intermesh with therecess in the other roll, said rolls being power driven and being adapted to impart an s-shaped cross section to an elongated metal strip moving between them, a pair of pressure shoes arranged to ensage opposite edge portions of said strip on opposite sides thereof adjacent to and in advance of said rolls, and. a pair of pressure rollers arranged to enga e opposite edge portions of said strip on opposite sides thereof adjacent to and following said rolls.

5. The combination in apparatus for forming Venetian blind slats, of a pair of forming rolls each provided with an annular projection and I an annular recess, the projection on one roll being arranged to intermesh with the recess in the other roll, said rolls being power driven and being adapted to impart an S-shaped cross section to an elongated metal strip moving between them, a pair of pressure shoes arranged to engage opposite edge portions of said stripon opposite sides thereof adjacent to and in advance of said rolls, a pair of pressure rollers arranged to engage opposite edge portions of said strip on opposite sides thereof adjacent to and following said rolls, and means for adjusting said shoes and said rollers transversely to the direction of travel of said strip.

6. The combination in apparatus for forming longitudinally and bending it to form an S- shaped cross section in the strip, means for supporting the strip in advance of the place of bending by means, engaging the concaved surfaces of the strip on opposite sides of its longitudinal center line, and means for supporting the strip following the place of bending by means engaging the concaved surfaces-ofthe strip on opposite sides of its longitudinal center line, whereby the lateral edge portions of the strip are stretched longitudinally.

7. The method of forming a metal strip ofder compression, and then moving-the strip longitudinally and bending it transversely into a cross section made up of a plurality of curvatures and simultaneously supporting the strips on the concave sides of said curvatures in advance of and following the place of transverse bending.

8. The method of forming a longitudinally straight Venetian blind slat of S-shaped cross section from an elongated metal strip having a central portion of greater length than its lateral edge portions, which comprises the operations of moving said strip longitudinally while bending successive portions of said strip into an S-shaped cross section, and confining said successive portions to that cross section while supporting the strip on its opposite surfaces on opposite sides of its longitudinal center line, whereby a straight slat of S-shaped cross section having parallel longitudinal edges is produced.

ALLEN B. WILSON. 

